With growing up and constant progressing of the solid-state lighting technique, the light-emitting diode has become a preferable solution in the nowaday illuminating engineering due to its features such as high efficiency, energy conservation, long life, and environment friendly, and has been applied in illuminating products increasingly. Significant reduction in energy consumption and achievable long and reliable operation are key factors which are drawing people's attention to the LED illuminating technique.
Direct current driving is applied in all the LED lamps, including LED tube lamps. In whatever case of direct power supply via alternating current mains or power supply via CCG or ECG, a power source adaptor, i.e., LED driving circuit is required to interpose between the alternating current mains, CCG and ECG, and the LED lamps. The driving circuit has a function of converting the power supply into direct current suitable for LED.
In designing LED driving circuits, especially in designing high power LED driving circuit, it is necessary to consider the problem of power factor correction (PFC) in order to avoid reducing the power factor and causing power factor pollution in the power grid due to the application of LED lamps. An active PFC circuit is operable by adding a switch conversion circuit between an input rectifier bridge and an output filter capacitor, which corrects the input current into a sine wave with identical phase to the input voltage and without distortion, making the power factor approach one. The active PFC converter is followed by the switching power supply of a DC-DC converter for supplying the direct current suitable for LED.
Almost all of the active PFC converters are boost-typed, for the main reason that there can be a smaller output current under condition of a certain output power, thus making it possible to reduce the capacity and volume of the output capacitor, and reduce the diameter of winding wires of boost inductance elements as well.
At present, what are commercially available are limited to LED illuminating devices, such as LEG tube lamps, which are compatible with the alternating current mains and CCG, and LED illuminating devices, such as LEG tube lamps, which can only use ECG power supply. In this situation, more and more attention are paid regarding how to be compatible with the alternating current mains, the CCG and the large kinds of ECG.